This invention relates to a material handling apparatus with an improved fail-safe brake system.
Numerous material handling devices such as crane-excavators and the like utilize a fail-safe brake for purposes of safety. Such a brake is automatically and normally biased into engaged position, and must be released by some positive action of the operator.
In a crawler type crane-excavator, a fail-safe brake is often applied to the crawler drive mechanism to prevent run-away of the machine if the operator becomes ill or accidentally mishandles the controls. Such brakes have usually been positioned low on the machine, adjacent the crawler mechanism for purposes of efficiency and machine stability.
Fail-safe brakes of the type used in heavy material handling machines have usually included a spring biased movable piston within the brake housing. A vent in the brake housing and extending between the outer end of the piston chamber and the outside has been necessary to permit piston movement and prevent lock-up of the brake mechanism. This vent has been disadvantageous in that it has permitted penetration of undesirable material into the brake housing itself, causing corrosion and undue wear of the brake. For example, crane-excavators are sometimes operated in flooded or high water areas wherein a major portion of the crawler and brake mechanism is submerged. Water and fine sludge will then pass inwardly through the vent, damaging the brake.
The concept of the present invention eliminates the need for a vent of the kind previously used, and still permits free movement of the brake piston. In addition, the invention contemplates a purging of the brake housing to remove contaminants from the brake elements, as well as lubrication of the said element, if desired.
In accordance with the invention, a port in the piston end of the brake housing is connected to an external source of pressurized air. A passage through the piston rod permits flow of this air to the opposite piston side, thereby equalizing the air forces thereon. The air intimately contacts the brake elements and biasing spring means and is discharged from adjacent the spring means to the outside through a one-way exhaust valve. When maximum purging is desired, the air discharge is disposed in the lowermost portion of the spring means. In addition, the pressurized air may be conditioned and also provided with a lubricant or the like therein to help maintain proper brake functioning and reduce the possibility of corrosion of the brake parts. The pressurized air supply is contemplated as being responsive to release of the brake.